Clean all of the oil residue up first. I like WD-40 for this purpose. This allows you to spot a new leak more easily in the future. Inspect the sending unit carefully, with the engine running. Sometimes the sender can fail and leak oil itself. It can be tricky to spot a leak sometimes as some leaks happen only during temperature transitions (like when an engine is warming up) so watch the engine when you start it and let it warm up while you determine that everything is ok.
You may have found your problem when you tightened the fitting. I do not use Teflon paste on pipe thread oil pressure fittings, Yanmar makes no mention of sealant in the service manual for our engine (3jh4e).
I am sure that backing down had no large impact on oil pressure unless you have other issues like a stuck oil pressure regulator and then you would see issues when the engine was cold and revved. Keep an eye on things and report back?
Bruce